Thought-controlled wheelchairs and nerve-controlled prosthetic arms are some of the latest innovations in bionics being discussed at a science conference in Washington.

The wheelchair can be directed by brain signals detected using a cap fitted to the user and is the work of scientists at the Ecole Polytechnique Federale de Lausanne in Switzerland (EPFL).

It is part of efforts to control machines directly via brain signals, which could lead to new devices for the paralysed and disabled.

Nerve surgery

The main focus of bionics to date has been on providing prosthetics for amputees. Prosthetic arms can now be controlled by nerve signals in the remaining arm, which can be picked up by electric sensors on the skin.

Those with arms amputated above the elbow, where important nerves have been severed, can also potentially control such devices, thanks to what is called "Targeted Muscle Reinnervation" surgery (TMR).

The surgery involves repositioning of nerves into unused muscles around the remaining arm or shoulder so that clear signals can be generated to drive the prosthetic via sensors on the skin surface.

Speaking at the annual conference of the American Association for the Advancement of Science (AAAS) in Washington, Professor Todd Kuiken of The Rehabilitation Institute of Chicago, which pioneered TMR surgery, told the BBC the next innovation may be bionic limbs which are able to "feel".

"If you touch the person on this 'reinnervated' skin, they feel their missing hand. Normal hot and cold, they feel it in their missing hand," he said. "So this is an exciting pathway for us to give sensory feedback; imagine putting sensors in their prosthetic hand to measure force."

Researchers are also looking to devise bionic limbs that can respond to multiple signals from the body - what is called "pattern recognition" - with some suggesting these could lead to bionic hands with individually controllable fingers.

But there is also now the prospect of devices for paralysed or severely disabled individuals with the arrival of brain-controlled devices, of which the thought-controlled wheelchair is just one example.

Professor Jose del R Millan and colleagues from EPFL, who have developed the wheelchair, brought with them to Washington a thought-controlled robot that a paralysed individual could control with brain signals.

"It could help disabled people by substituting some of those lost motor capabilities," said Professor Millan. "People could be 'virtually elsewhere' because they can see what the robot sees."Elective amputation

Such is the pace of progress with bionics that there are now patients choosing bionic limbs over real ones.

Last year, a young Austrian man named "Patrick", who sustained traumatic injuries after being electrocuted at work, opted for the elective amputation of his left hand, which no longer had any function. He has now been fitted with a prosthetic arm with which he can grasp and lift objects using nerve signals in his amputated arm.

His surgeon, Professor Oskar Aszmann of the Medical University of Vienna, says the use of a hybrid bionic hand attached to his dysfunctional hand convinced him of the benefits of the amputation.

"By then he realised he'd probably be better off with a bionic hand rather than his own flesh and blood hand," Professor Aszmann told the BBC after a recent lecture at the Royal Society of Medicine in London.

"For him the most important thing is not really the loss of his non-functional piece of anatomy but the gain of functionality. He could see after two hours that he could do tasks that he hadn't done for two or three years."

Later this year, a second of Professor Aszmann's patients will undergo elective amputation in favour of a bionic replacement.